Issue 9, August 12, 2021

Dogwood sawfly

Left: Dogwood sawfly feeding injury, Travis Cleveland, University of Illinois at Urbana-Champaign
Right: Dogwood sawfly larva close-up, Travis Cleveland, University of Illinois at Urbana-Champaign

Dogwood sawflies (Macremphytus tarsatus) are native to much of the eastern US and Canada. They are a wasp species whose caterpillar-like larvae feed on the foliage of dogwoods in groups.

Dogwood adults emerge and lay eggs in mid-late spring. The eggs are laid on the underside of dogwood leaves along leaf veins. The larvae hatch and begin to feed on dogwood foliage in late-spring. The larvae often go unnoticed until late summer, when both the larvae and their injury become obvious. Most of the damage occurs later in the season and doesn’t impact overall plant health unless there are high populations of larvae.

Dogwood sawfly eggs on leaf, Bruce Watt, University of Maine, Bugwood.org

Scouting for dogwood sawfly larvae can be tricky. Their color and markings can differ greatly, giving the impression that there are multiple insect species feeding on the plant. The larvae may be green with black spots, white with black spots, or white and covered in waxy material. Larvae in their last instar (growth stage) are usually yellow with dark markings down their back.

Left: Dogwood sawfly larva green, Travis Cleveland, University of Illinois at Urbana-Champaign
Center: Waxy middle instar dogwood sawfly larvae, Bruce Watt, University of Maine, Bugwood.org
Right: Older dogwood sawfly larvae, Travis Cleveland, University of Illinois at Urbana-Champaign

Hand picking insects or knocking them off the plants are among the best ways to control older larvae since they are easy to spot on the plants. Insecticides such as carbaryl (Sevin) or pyrethroids can be applied when significant defoliation occurs. However, insecticides are most effective on young larvae. Since sawfly larvae are not true caterpillars, Btk (Bacillus thuringiensis kurstaki) products will not kill them.

Author:
Sarah Hughson

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